Synthetic turf

ABSTRACT

The present invention provides new types of synthetic turf. The synthetic turf includes a pile fabric having a backing ( 1 ) and tufts ( 2 ) projecting therefrom. In one embodiment, at least a number of the tufts are made of a composite yarn formed by at least one fibrillated yarn ( 6 ) together with a number of individual filament yarns ( 7 ), in particular with so-called monofilament or monotape yarns. The fibrillated yarn and the individual filament yarns are preferably made of polyethylene so that the synthetic turf is sliding-friendly. In another embodiment, at least a number of the tufts are made of a composite yarn formed by monotape yarns twisted together with a number of the monofilament yarns. The monofilament and monotape yarns are preferably made of polyethylene so that the synthetic turf is sliding-friendly. The combination of a fibrillated yarn and individual filament yarns or the combination of monofilament and monotape yarns in a composite yarn allows immediate achievement of the look of natural grass, that is, without post-fibrillation, and avoids any visible difference in wear pattern between the different types of yarns. In another embodiment, the invention also provides improved particulate material for use as infill material for top-dressing a synthetic turf.

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. § 371 ofInternational Application PCT/EP2004/002301, filed Mar. 5, 2004, whichclaims priority of EP 03447049.2, filed Mar. 5, 2003.

FIELD OF THE INVENTION

The present invention relates to a synthetic turf comprising a pilefabric having a backing and tufts projecting therefrom, the tuftscomprising portions of individual filament yarns and portions of atleast one fibrillated yarn which is comprised of a tape showinglongitudinal slits forming laterally interconnected filaments, theindividual filament yarns and the interconnected filaments havingdimensions such as to resemble blades of grass. The present inventionalso relates to a synthetic turf comprising a pile fabric having abacking and tufts projecting therefrom, the tufts comprising portions ofindividual filament yarns comprising extruded monofilament yarns andmonotape yarns, the monofilament yarns and monotape yarns havingdimensions such as to resemble blades of grass.

BACKGROUND OF THE INVENTION

Synthetic or artificial turf is used more and more to replace naturalgrass turf on playing surfaces, in particular on sport fields likefields for playing football, rugby, tennis, golf, hockey, baseball etc.In order to provide a somewhat resilient surface, a top-dressing can beapplied onto the backing layer. The thickness of this top-dressing issmaller than the height of the tufts so that the grass-like filamentsproject above the top-dressing. A top-dressed synthetic turf isdisclosed for example in U.S. Pat. No. 4,337,283.

In practice, the top-dressing of so-called third generation syntheticgrass fields usually consists of a hard layer and on top a layer ofresilient granules, as for instance disclosed in WO 01/98589. Thisdocument discloses a synthetic grass assembly for installation on asupporting substrate comprising a pile fabric with a flexible sheetbacking and a plurality of upstanding synthetic ribbons of a selectedlength. An infill layer of particulate material, selected from the groupconsisting of hard and resilient granules, is disposed interstitiallybetween the upstanding ribbons upon the upper surface of the backingwith a depth less than the length of the ribbons. The infill layer inparticular comprises a bottom course of hard granules, disposed upon thetop surface of the backing and a top course substantially exclusively ofresilient granules disposed upon the bottom course.

Frequently applied resilient granular materials that may be used asinfill materials may include mixtures of granulated rubber particleslike SBR (styrene butadiene rubber) recycled from car tires, EPDM(ethylene-propylene-diene monomer), other vulcanised rubbers or rubberrecycled form belts. However, these rubbers have several importantdisadvantages. In particular, they can not be re-used and have a limitedlife span since they loose there properties throughout use. Furthermore,the use of this type of rubbers in a top-dressing layer of a syntheticturf does not provide sufficient resilience or shock absorption. Most ofthe synthetic turf for football fields consists nowadays of pile fabricmade of fibrillated yarn. This fibrillated yarn is usually made ofpolyethylene or of a mixture of polyethylene and polypropylene and istufted on a machine with a needle distance of between ⅝″ (≈15.8 mm) and3/16″ (≈4.7 mm). A drawback of the used fibrillated yarns is that theyhave a relatively low wear resistance and that a post-fibrillation witha rigid (steel) brush is required after having laid the synthetic turf.The post-fibrillation is required to separate the different filaments ofthe fibrillated yarn from one another in order to hide the topdressingbetter from view and in order to achieve the look of natural grass. Adrawback of such a post-fibrillation is however that the pile yarn isdamaged. In addition to synthetic turf made of fibrillated yarn, thereis also synthetic turf made of so-called monotape or monofilament yarn.The difference between monotape and monofilament yarn is that, for theproduction of monotape yarn, a film is extruded which is cut into smallbands whilst for the production of monofilament yarn the bands formingthe monofilaments are separately extruded. A drawback of synthetic turfmade of monotape or monofilaments is that the top-dressing is lessstabilised against shifting and/or erosion and that the rubber granulesare less hampered from jumping up. In practice, most of the monotape ormonofilament yarns used to make artificial turf are moreover made ofpolypropylene which offers better resilience properties thanpolyethylene but which has a higher coefficient of friction so thatburning wounds occur much quicker, for example when falling or making asliding on the synthetic turf surface. Synthetic turfs formed by yarnsmade of polyamide have been reported in the art, and are for instancedisclosed in U.S. Pat. No. 3,940,522 and WO 99/04074. In U.S. Pat. No.3,940,522 synthetic turfs are described comprising grass-like syntheticfibers and crimped fibers. One or more of the grass-like fibers arecombined with an appropriate multi-fiber strand of crimped and/orlatently crimpable fibers. The fibers are made of polyamides such asnylon 6, nylon 6,6, nylon 6,10, nylon 6,12, and copolymers and blends ofthese. WO 99/04074 discloses yarns containing polyamide in combinationwith a polyolefin compound for producing artificial grass. A majordisadvantage of this type of synthetic turfs formed by yarns made ofpolyamide is that the turfs show high sliding resistance, and a highcoefficient of friction so that burning wounds occur much quicker, forexample when falling or making a sliding on the synthetic turf surface.

In practice there is also a synthetic turf on the market comprisingalternating rows of tufts made of fibrillated yarn and rows of tuftsmade of monofilament yarns. An advantage of such a combination is thatthe turf has an appearance which immediately resembles more naturalgrass. However, a post-fibrillation or several months of wear is stillrequired to make the synthetic turf look like natural grass. A furtherdrawback of this combination is that, due to the fact that thefibrillated yarn wears more quickly than the monofilament yarns, thedifference in wear pattern between the fibrillated yarn and themonofilament yarns can clearly be seen after a more prolonged time ofuse.

It is an object of the present invention to provide a new type ofsynthetic turf that has more the look of natural grass, but which solvesthe problem of the difference in wear pattern which can be seen after aprolonged time of use of the prior art synthetic turf. It is anotherobject of the invention to provide a synthetic turf having improvedresilience, shock absorption and safeness (e.g. reducing the risks forskin burns when making a sliding on the turf surface).

SUMMARY OF THE INVENTION

To this end, the present invention provides in a first embodiment asynthetic turf which comprises a combination of fibrillated yarn andindividual yarns. The synthetic turf is characterised according to theinvention in that at least a number of said tufts are made of acomposite yarn formed by said fibrillated yarn twined together with anumber of said individual filament yarns.

Due to the fact that the fibrillated yarn and the individual filamentyarns are combined in one composite yarn, no difference in wear patterncan be seen, at least not without a close inspection of the tufts.Moreover, it was found that due to the use of a composite yarn whereinthe fibrillated yarn is twined together with the individual filamentyarns, the synthetic turf immediately resembles better natural grass. Inthe synthetic grass surface, the fibrillated yarn portions are indeedmore homogeneously mixed with the individual filament yarn portions sothat no post-fibrillation is needed or so that the synthetic turf hasnot to be subjected to wear, or only for a short period of time, toachieve the appearance of natural grass.

In a preferred embodiment of the synthetic turf according to theinvention, the fibrillated yarn has a yarn number which is selected,together with the number of individual filament yarns in the compositeyarn, in such a manner that, without post-fibrillation of the free endsof the fibrillated yarn, the tufts made of the composite yarn resemblegrass.

The composite yarn preferably comprises 4 to 10 individual filamentyarns, and more preferably 6 to 8 individual filament yarns whilst thefibrillated yarn has preferably a yarn number higher than 2000, andpreferably higher than 5000, but smaller than 11000, and preferablysmaller than 8500 dtex.

In a further preferred embodiment of the synthetic turf according to theinvention, at least the fibrillated yarn of said composite yarn, andpreferably also at least a number of said individual filament yarns ofsaid composite yarn, most preferably all of them, are made ofpolyethylene.

In another embodiment, the present invention provides a new type ofsynthetic turf which comprises a combination of monotape yarns andmonofilament yarns. The synthetic turf is characterised according to theinvention in that at least a number of said tufts are made of acomposite yarn formed by said monotape yarns twisted together with anumber of said monofilament yarns.

Due to the fact that the monotape yarns and the monofilament yarns arecombined in one composite yarn, less difference in wear pattern even incomparison with the combination fibrillated yarn and monofilament yarncan be seen. This combination strongly resembles natural grass.

The composite yarn preferably comprises 1 to 6, and more preferably 1 to3 monotape yarns whilst the monotape yarn has preferably a yarn numberhigher than 1000, and preferably higher than 2000 dtex, but smaller than5000 dtex, and preferably smaller than 3000 dtex. The composite yarn haspreferably a yarn number higher than 8000, and preferably higher than9000 dtex, but smaller than 20000 dtex, and preferably smaller than15000 dtex.

In a further preferred embodiment of the synthetic turf according to theinvention, at least the monotape yarn of said composite yarn andpreferably also at least a number of said monofilament yarns of saidcomposite yarn, most preferably all of them, are made of polyethylene.

An important advantage of these embodiments is that the synthetic turfcan be rendered more sliding-friendly, i.e. its coefficient of frictioncan be made smaller than for example the coefficient of friction ofpolypropylene so that burning wounds arise less quickly. Due to the factthat the individual filament yarns are twined together with afibrillated yarn in the composite yarn, the smaller resilienceproperties of the polyethylene yarns compared to for examplepolypropylene yarns, are partially compensated for by the supportoffered by the fibrillated yarn. On the other hand, some of theindividual filament yarns may be made of another polymer, in particularof a polymer which offers a better resiliency and/or which has a betterwear resistance. Another advantage of the use of fibrillated andindividual filament yarns which are all made of polyethylene instead ofa combination of polyethylene and polypropylene is that the syntheticturf is easier to recycle. The synthetic turf has moreover a softertouch.

In a further embodiment the present invention also relates to asynthetic turf. characterised in that it is top-dressed with a layer ofparticulate (infill) material. In another embodiment, the inventionprovides for a particulate material which is particularly suitable forbeing used as infill material in synthetic turfs. The infill materialcomprises a polyolefin elastomer, preferably a low densityethylene/octene co-polymer. In a preferred embodiment, the particulateinfill material is filled with filler material selected from the groupcomprising chalk or clay. Preferably, the amount of filler material insaid infill material is comprised between 50 and 60% by weight and theamount of polyolefin elastomer in said infill material is comprisedbetween 40 and 50% by weight.

In another embodiment, the present invention relates to a composite yarncharacterized in that said composite yarn is formed by a fibrillatedyarn twined together with a number of individual filament yarns. In yetanother embodiment, the present invention relates to a composite yarncharacterized in that said composite yarn is formed by monotape yarnstwisted together with a number of monofilament yarns.

The present invention further relates to the use of the above-mentionedcomposite yarns as tufts in a synthetic turf. The present invention alsorelates to the use of the above-mentioned composite yarns as tufts in anatural grass system for reinforcing and stabilising natural grassroots.

Other particularities and advantages of the invention will becomeapparent from the following description of some particular embodimentsof the synthetic turf according to the present invention. The referencenumerals used in this description relate to the annexed drawings.

DETAILED DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic side elevational view on a fibrillated yarn towhich a lateral tension is exerted.

FIG. 2 is a schematic view on six monofilament yarns.

FIG. 3 is a side elevational view on a composite yarn composed of afibrillated yarn as illustrated in FIG. 1 and six monofilament yarns asillustrated in FIG. 2, the fibrillated yarn and the monofilament yarnsbeing twined together so that the fibrillated yarn is twisted on theoutside around the monofilament yarns.

FIG. 4 is a schematic cross-sectional view through a synthetic turfcomprising a backing layer and tufts made of the composite yarnillustrated in FIG. 3, the synthetic turf being further filled with atop-dressing.

DETAILED DESCRIPTION OF THE INVENTION

The synthetic or artificial turf illustrated in FIG. 4 comprises aflexible backing layer 1 provided with rows of tufts 2 made of acomposite yarn 3. The synthetic turf is more particularly formed by acut pile fabric. For producing such a pile fabric; the composite orcombined yarn 3 is fed through the needles of a tufting machine and isinserted through the backing layer to form pile loops. The pile loopsare then cut by knives to form the cut pile fabric and latex, foam oranother adhesive material is applied to the underside of the fabric tosecure the pile fibres to the backing. The backing layer 1 may consistfor example of a woven polypropylene sheet and a glass fibre nettingfixed by means of the above described adhesive material to thepolypropylene sheet. Since the backing layer is no essential feature ofthe present invention, no further details will be described thereof.

In an embodiment, in the synthetic turf according to the invention, atleast a number of the tufts 2 are made of a composite yarn 3 which isformed by at least one fibrillated yarn 6 twined together with a numberof individual filament yarns 7. The fibrillated yarn 6 and theindividual filament yarns 7 are preferably made of polyethylene,although it is possible to make the individual filament yarns, or atleast some of them, of another polymer, for example of a polymer whichprovides a higher resiliency and/or which has better wear properties.Especially when making all the yarns of polyethylene, the synthetic turfhas a smaller coefficient of friction so that burning wounds arise lessquickly. The synthetic turf is moreover easier to recycle. Furthermore,since all the filaments are made of the same material, it is easier toavoid colour differences. Another advantage of polyethylene is that ithas a higher wear resistance than for example polypropylene. For askilled person it is clear that the polyethylene contains certainadditives such as UV and heat stabilisers, colour pigments and/orcolorants. Optionally, it may even contain small amounts of one or moreother polymers, more particularly in an amount of less than 10% byweight, preferably less than 5% by weight.

The individual filaments yarns 7 may be so-called monotape yarnsproduced by cutting an extruded film into narrow bands. The extrudedfilm is preferably led over stretching drums to organise the moleculesso that the strength of the film is increased. Instead of firstproducing a film, a more preferred way to produce the individualfilament yarns is to extrude them directly into the desired size so thatno cutting operation is required. In this way, preferably also after astretching step, a so-called monofilament yarn is obtained. FIG. 2illustrates six monofilament yarns 7. These yarns have such a thicknessand a width that they resemble grass blades. The width of the yarns ispreferably smaller than 4 mm, more preferably smaller than 3 mm, andmost preferably smaller than 2 mm, but larger than 0.8 mm, preferablylarger than 1 mm. A fine, natural grass look is for example obtainedwhen the width of the filaments comprises about 1.4 mm. The thickness ofthe individual filament yarns 7 is not only important to achieve thelook of natural grass, but also to achieve the required resilienceproperties. The individual filament yarns will usually have a thicknessof between: 100 and 200 μm. Especially for polyethylene yarns, whichprovide less resiliency than for example polypropylene yarns, theindividual filament yarns have preferably a thickness larger than 125μm, and more preferably a thickness larger than 135 μm. Good resultshave for example been obtained when the thickness of the individualfilament yarns comprises about 160 μm. The yarn number of the individualfilament yarns will usually be comprised between 1000 and 3000 dtex inorder to resemble grass, and will more preferably be comprised between1100 and 1700 dtex. The individual filament yarns may have for example ayarn number of about 1400 dtex.

Turning now to FIG. 1 there is illustrated an example of a fibrillatedyarn 6. Such a fibrillated yarn is produced starting from an extrudedfilm which is first cut into bands. In these bands longitudinal slits 8are made so that laterally interconnected filaments 9 are formed. Theseslits can be made for example by means of a drum provided with needles(and rotated at a speed different from the speed of the film led overthis drum) or teeth as disclosed in U.S. Pat. No. 3,496,259. In FIG. 1the fibrillated yarn is shown in a laterally stretched state so that theslits are drawn open and a structure resembling a honeycomb is obtained.

The fibrillated yarn 6 has for example a total width of 9 mm, the slits8 being arranged so that the interconnected filaments 9 have a widthwhich is preferably somewhat smaller than the width of the individualfilament yarns. Moreover, the slits are preferably not provided on thesame mutual distances so that broader filaments are separated bynarrower filaments which provide for a looser connection between thebroader filaments. By selecting a smaller width of the filaments and/ora looser connection between the filaments, the filaments becomeimmediately spread in a random manner after the tufting operation thuscontributing to achieving immediately the natural look of grass. Theyarn number of the fibrillated yarn will normally be higher than 2000dtex and will usually be comprised between 5000 and 11000 dtex, andpreferably between 5000 and 8500 dtex. When using a fibrillated yarnwith a smaller yarn number, the composite yarn may contain moreindividual filament yarns since the maximum yarn number of the compositeyarn is limited by the tufting technique. The composite yarn can forexample be made with three fibrillated yarns, having each a yarn numberof 2000 dtex. These fibrillated yarns can first be twined together andcan subsequently, in a second twining operation, be twined together withthe individual filament yarns. The thickness of the fibrillated yarn ispreferably comprised between 60 and 100 μm, and more preferably between70 and 90 μm. Since the filaments of the fibrillated yarn areinterconnected, the thickness thereof may be smaller than the thicknessof the individual filament yarns. A predetermined minimum thickness ishowever preferred in view of the increased wear resistance (mechanicalwear and/or heat and UV degradation) and the increased resiliencyobtained with a larger thickness.

By making the tufts of the pile fabric as described hereabove by meansof a composite yarn 3, the yarn number of the fibrillated yarn 6 and thenumber of individual filament yarns 7 can be easily selected in such amanner that, without post-fibrillation, the pile fabric immediatelyresembles grass.

The composite yarn 3 will usually comprise 4 to 10, preferably 6 to 8,individual filament yarns 7. It may comprise more than one fibrillatedyarn 6 but preference is given to the presence of only one fibrillatedyarn. When only one fibrillated yarn is present, it may have a largeryarn number so that the filaments are better connected with one another.The yarn number of the composite yarn is indeed preferably formed for atleast 40%, more preferably for at least 50%, by the individual filamentyarns in view of resembling immediately as much as possible naturalgrass. On the other hand, in view of better stabilising thetop-dressing, preferably at least 30%, and more preferably at least 35%of the yarn number of the composite yarn is formed by the fibrillatedyarn or yarns. In order to be able to provide, on the one hand, afibrillated yarn with a relatively high yarn number and, on the otherhand, a relatively large number of individual filament yarns, the yarnnumber of the composite yarn 3 will usually be larger than 9000, andpreferably larger than 11000 dtex. Due to the limitations of the tuftingmachines, the yarn number of the composite yarn will usually be smallerthan 20000 and more particularly smaller than 17000 dtex.

In the composite yarn according to the invention the fibrillated yarn 6is preferably twined around the individual filament yarns 7 so that thecomposite yarn has an outer surface which is mainly formed by thefibrillated yarn.

In order to make the composite yarn 3, the individual filament yarns 7and the fibrillated yarn 6 are twined together. The word. “twined” hasto be understood here in its broadest meaning and includes for examplealso a simple twisting of the yarns. The composite yarn may further betwined in the S or Z direction. The number of windings (per meter)during the twining process must be limited in such a manner that thefilaments will spread themselves again after the tufting process. Thiscan be determined experimentally. When twining the composite yarn, thefibrillated yarn is preferably twined around the individual filamentyarns so that the composite yarn has an outer surface which is mainlyformed by the fibrillated yarn. This is clearly illustrated in FIG. 3.An advantage of such a way of twining is that the composite yarn can betufted more easily and that, when applying the adhesive material on thebacking layer, the filaments are kept better in place so that a niceback finishing is obtained.

In another embodiment, in the synthetic turf according to the invention,at least a number of the tufts are made of a composite yarn which isformed by monotape yarn twisted together with a number of monofilamentyarns. The monotape yarn and the monofilament yarns are preferably madeof polyethylene, although it is possible to make the monofilament yarns,or at least some of them, of another polymer, for example of a polymerwhich provides a higher resiliency and/or which has better wearproperties. Especially when making all the yarns of polyethylene, thesynthetic turf has a smaller coefficient of friction so that burningwounds arise less quickly. The synthetic turf is moreover easier torecycle. Furthermore, since all the filaments are made of the samematerial, it is easier to avoid colour differences. Another advantage ofpolyethylene is that it has a higher wear resistance than for examplepolypropylene. For a skilled person it is clear that the polyethylenecontains certain additives such as UV and heat stabilisers, colourpigments and/or colorants. Optionally, it may even contain small amountsof one or more other polymers, more particularly in an amount of lessthan 10% by weight, preferably less than 5% by weight.

The monotape yarns and the monofilament yarns applied in the combinedyarn have such a thickness and a width as to resemble grass blades. Thewidth of the monotape yarn is preferably larger than 1.5 mm, morepreferably larger than 2 mm and preferably smaller than 3 mm. Thethickness of monotape yarn is not only important to achieve the look ofnatural grass, but also to achieve the required resilience properties.The monotape yarns will usually have a thickness of between 100 and 150μm, and preferably of between 100 and 120 μm. The yarn number of themonotape yarns will usually be comprised between 1000 and 5000 dtex inorder to resemble grass, and will more preferably be comprised between2000 and 3000 dtex.

The composite yarn will usually comprise 1 to 6 and preferably 1 to 3monotape yarns and 2 to 8, and preferably 4 to 6 monofilament yarns. Theyarn number of the composite yarn is preferably formed for at least 30%,more preferably for at least 40% by the monotape yarn in view ofresembling immediately as much as possible natural grass. Morepreferably, the yarn number of the composite yarn is formed for at least40% and at most 50% by the monotape yarn. The yarn number of thecomposite yarn will usually be higher than 8000, and preferably higherthan 9000 dtex. Due to the limitations of the tufting machines, the yarnnumber of the composite yarn will usually be smaller than 20000 and moreparticularly smaller than 15000 dtex.

In another preferred embodiment, in the composite yarn according to theinvention the monotape yarn is preferably twined around the monofilamentyarns so that the composite yarn has an outer surface which is mainlyformed by the monotape yarn.

In view of the relatively high yarn number of the composite yarnsaccording to the present invention, the distances between the rows oftufts may be larger. Usually, the mutual distances between the rows willbe comprised between 8 and 24 mm, preferably between 10 and 20 mm, andmore preferably between 12 and 18 mm. A mutual distance of 16 mm orlarger is most preferred.

In order to enable the presence of a top-dressing, the tufts 2 of thesynthetic turf have preferably an average height larger than 30 mm andmore preferably an average height larger than 40 mm. In this way, thetufts of the pile layer still project over a sufficient distance abovethe top-dressing. The average height of the tufts 2 is usually smallerthan 75 mm and is preferably comprised between 50 and 60 mm. The averageheight of the tufts is to be determined by measuring and totalling theheight of the different filaments and dividing the achieved number bythe number of filaments.

Synthetic turf is generally used to replace natural grass on playingsurfaces. In order to provide a somewhat resilient surface, atop-dressing can be applied onto the backing layer. The synthetic turfaccording to the present invention is preferably arranged to betop-dressed with a layer of at least one particulate material. Thethickness of this top-dressing is smaller than the height of the tuftsso that the grass-like fibres as mentioned above project above thetop-dressing. Preferably the thickness of this top-dressing comprisesbetween 0.5 and 3.0 cm and more preferably between 1.0 and 2.0 cm.

In practice, the top-dressing of so-called synthetic grass fieldsusually consists of a hard layer and on top a layer of resilientgranules including mixtures of granulated rubber particles like recycledSBR from car tires, EPDM, other vulcanised rubbers, recycled rubber formbelts and even thermoplastic elastomers based on SEBS(styrene-ethylene-butadiene-styrene). In the embodiment of FIG. 4, thesynthetic turf is first filled with a layer of sand 4 and, on top ofthat, with a layer of rubber granules 5. In this way, a resilient,non-abrasive surface is achieved.

Presently, about 90% of the infill used for football pitches is based onSBR rubber recycled from truck tyres. However, this kind of rubber has anumber of disadvantages including the possibility of migration of theexisting aromatic oils which will attack the polyolefine yarns, and therelease of an unpleasant smell above 25° C. Furthermore, the possibilityexists that a field can be heated up to 70° C., due to the black carbonin the rubber, which might be dangerous since skin burns can be affectedby T° above 60° C. Other disadvantages include that the leaching of zinc(vulcanisation process) does not fulfil standard norms and that therubber is not fire retardant. Also, in this kind of rubber sulphur maybe present, which attacks the UV stabilisation of the yarn. When therubber is not properly processed, steel may be formed. Also, the use ofthis kind of rubber only provides black colours which give an unnaturallook to the synthetic turf.

Because of all these disadvantages of the recycled black rubber fromtires, new alternatives were introduced. New compounds/producedmaterials such as EPDM or TPVs (thermoplastic vulcanizates) in which nosulphur with zinc oxide curing system is used were applied. Advantagesof these rubbers include that they can be coloured in any colour. Beigecolours give a temperature which is 10 to 20° C. lower at sunny weatherduring summer than previously used rubber. The rubbers fulfilrequirements of standard norm (DIN 18035-7) and are fire retarding.However, some important disadvantages of these rubbers remain that therubbers are not recyclable, that they do not provide optimised playingcharacteristics, that they give a bad smell, and that they have a veryhigh filler content of more than 80%. Furthermore, granules of a badquality of EPDM rubber loose their shape and are melted together afterseveral months.

In order to overcome this problem, the present invention provides asynthetic turf, characterised in that it is top-dressed with a layer ofparticulate infill material comprising a polyolefin elastomer.Preferably said polyolefin elastomer is a low density ethylene/octeneco-polymer. However, it should be clear from the present invention thatalso other polyolefin elastomers, such as but not limited to EPM may beapplied.

Referring now to the low density ethylene/octene co-polymer, the moreefficient and consistent incorporation of octene co-monomer into apolyethylene backbone, made possible by a metallocene catalyst, resultsin lower density and more narrowly defined polymers with a range ofbenefits including flexural modulus similar to elastomers, thermoplasticbehaviour without plasticizers, exceptional compatibility with otherpolyolefines providing the opportunity to blend with EPM, exceptionaltoughness, puncture resistance, flexibility even at very low temperature(below −20° C.), very low extractable and surface softness. Theresilient infill based on ethylene/octene co-polymer bridges the gapbetween plastics and elastomers and as such combines many of thephysical properties of a rubber with the processing advantages of athermoplastic. The ethylene/octene copolymers are at the extremeperformance end in terms of overall toughness.

The resilient infill material, in particular based on ethylene/octenecopolymer, can be filled with a filler, preferably chalk or clay, toreduce the costs.

The infill material is preferably provided in the form of granules,which can be round, spherical or angular, and which are preferably roundor spherical. Preferably, the particulate material comprises granulesconsisting of polyolefin elastomer and filler.

The amount of polyolefine elastomer in the resilient infill granules ispreferably minimum between 20%-60% and maximum between 40%-100% byweight and more preferably minimum between 30%-50% and maximum between40%-50% by weight.

In another preferred embodiment, the synthetic turf according to theinvention is characterised in that the amount of filler material in saidparticulate material is comprised between 50 and 60% by weight and thatthe amount of polyolefin elastomer in said particulate material iscomprised between 40 and 50% by weight.

In a further preferred embodiment, the resilient infill granules basedon ethylene/octene copolymer can be blended with EPM (ethylene propylenecopolymer). The amount of EPM preferably comprises maximum between0%-20% by weight more preferably maximum between 0%-5% by weight. Ahigher amount of EPM will affect the mechanical properties.

The diameter of the resilient infill granules can be between 0.5 and 3mm, and preferably between 0.5 and 2.5 mm, and more preferably between1.0 and 2.5 mm. The compound density of the resilient infill granules isbetween 1.3 and 1.5 kg/dm³. The bulk density of the resilient infillgranules is between 0.6 and 1.0 kg/dm³.

Other features are constant granulometry, dust free, the fact that thematerial is not recycled, not milled from scraps, the thermoplasticelastomer does not need vulcanisation, is recyclable, and can be re-usedat end-life, and is thus ecological durable, the infill granules are UVand Ozone stable, non-toxic and not allergic, heavy metal free, PVC andphthalate free and not reactive in tight contact with PP and PE of theartificial turf. The present particulate material is particularlysuitable for use as infill material in synthetic turf and in particularfor top-dressing a synthetic turf.

The resilient infill system according to the invention will retain itsproperties throughout use without compaction of the infill material.Furthermore, the infill system in accordance with the present invention,in combination with the synthetic turfs according to the invention,permits to improve playing conditions and to reach natural grasscharacteristics and further players acceptance. The synthetic turf,provided with a top-dressed layer according to the present inventionfulfils the FIFA and UEFA requirements based on shock absorption; energyrestitution; ball bounce and ball roll. The present infill systemeliminates all leaching problems and provides a resilient infill whichsatisfies the ecological requirements and playing properties similar tothose of natural grass.

In another embodiment, the present invention relates to the use of acomposite yarn formed by a fibrillated yarn twined together with anumber of individual filament yarns and to the use of a composite yarnformed by monotape yarns twisted together with a number of monofilamentyarns as tufts in a synthetic turf.

In addition, the above-mentioned composite yarns can also be applied ina natural grass system. The present composite yarns may be applied innatural grass systems comprising grass tiles with roots for reinforcingand stabilising the natural turf. In practice, the synthetic yarns maybe inserted below the grass surface for root reinforcement andadditional wear resistance, while not interfering with the naturalnessof the playing grass surface itself. The synthetic yarns can be sewninto natural grass sod. The grass roots of the natural system intertwinewith the tufts of composite yarns and thereby become reinforced andstabilised. The roots of the natural grass use the synthetic yarns as ananchor and soil stabiliser to help prevent field stress from excessiveplay. The grass roots become entwined with the synthetic yarns, which,in turn hold the grass in place and the new growth replaces the wornareas of grass.

EXAMPLE 1

A composite yarn 3 was first made by twining one fibrillated yarn 6around six monofilament yarns 7. The fibrillated yarn had a yarn numberof 6600 dtex and a thickness of 80 μm. The slits were arranged on suchmutual distances d that the filaments had varying widths, moreparticularly width varying between about 0.1 mm and about 1.2 mm. Themonofilament yarns each had a yarn number of 1400 dtex, a thickness of160 μm and a width of 1.4 mm. The yarn number of the composite yarncomprised 15000 dtex. The different yarns were all made of polyethylenecontaining UV and heat stabilisers and a green pigment. The compositeyarn was tufted on a backing layer consisting of a woven polypropylenelayer and a glass fibre netting. The needle distance of the tuftingmachine was set at ⅝″. The tufts had an average height h of about 5 cm.A latex adhesive was applied on the back of the backing layer to fix thetufts. The achieved synthetic grass is illustrated in FIG. 4. In thecross-sectional view of this figure, only one portion of the compositeyarn is shown for each tuft. In practice, each tuft comprises, due tothe tufting technique, two portions of the composite yarn, the filamentsof both portions being intermixed with one another. To finish thesynthetic turf, it was filled with a layer of sand 30 and subsequentlywith a layer of rubber granules. The synthetic turf immediatelyresembled natural grass, i.e. no post-fibrillation or wear was necessaryto achieve this look.

EXAMPLE 2

A composite yarn was made by twining two monotapes around fourmonofilament yarns. The monotape yarn had a yarn number of 2200 dtex anda thickness of 100 μm. The width of the monotape yarn was 2.5 mm. Themonofilament yarn had a yarn number of 1400 dtex and a thickness of 160μm. The width of the monofilament was 1.4 mm. The yarn number of thecomposite yarn was 10000 dtex. The composite yarn was tufted on abacking layer consisting of a woven polypropylene layer and a glassfibre netting. A latex adhesive was applied on the back of the backinglayer to fix the tufts. The synthetic turf immediately resembled naturalgrass, i.e. no post-fibrillation or wear was necessary to achieve thislook.

From the above given description of some preferred embodiments of thesynthetic turf according to the invention, it will be clear that furthermodifications can be applied thereto provided they still fall within thescope of the invention as determined by the annexed claims.

Instead of using the twined composite yarn directly for tufting thesynthetic turf, it can for example first be knitted-deknitted to achievea frizzled structure. The rows of tufts do further not all have to bemade of the composite yarn but some rows could for example be made ofmonofilament yarns. To achieve the most optimal stabilising effect, andin order to avoid any difference in wear pattern, all the rows of tuftsare however preferably made of the composite yarn.

1. A synthetic turf comprising a pile fabric having a backing and tuftsprojecting therefrom, the tufts comprising portions of individualfilament yarns and portions of at least one fibrillated yarn which iscomprised of a tape showing longitudinal slits forming laterallyinterconnected filaments, wherein at least a number of said tufts aremade of a composite yarn formed by said fibrillated yarn twined togetherwith a number of said individual filament yarns, wherein the fibrillatedyarn of said composite yarn and also at least a number of saidindividual filament yarns of said composite yarn, are made ofpolyethylene, and wherein in said composite yarn said fibrillated yarnis twined around the individual filament yarns so that the compositeyarn has an outer surface which is mainly formed by the fibrillatedyarn.
 2. The synthetic turf according to claim 1, wherein saidfibrillated yarn has a yarn number which is selected, together with thenumber of individual filament yarns in said composite yarn, in such amanner that, without post-fibrillation of the free ends of saidfibrillated yarn, the tufts made of the composite yarn resemble grass.3. The synthetic turf according to claim 1, wherein said composite yarncomprises 4 to 10 individual filament yarns.
 4. The synthetic turfaccording to claim 1, wherein said individual filament yarns each have ayarn number of between 1000 and 3000 dtex.
 5. The synthetic turfaccording to claim 1, wherein said individual filament yarns have athickness of between 100 and 200 μm.
 6. The synthetic turf according toclaim 1, wherein said fibrillated yarn has a yarn number higher than2000 dtex.
 7. The synthetic turf according to claim 1, wherein saidfibrillated yarn has a thickness of between 60 and 100 μm.
 8. Thesynthetic turf according to claim 1, wherein said composite yarn has ayarn number larger than 9000 dtex, and smaller than 20000 dtex.
 9. Thesynthetic turf according to claim 1, wherein said composite yarn has ayarn number, at least 40% of which, is formed by said individualfilament yarns, said fibrillated yarn (6) forming preferably at least30%, of the yarn number of the composite yarn.
 10. The synthetic turfaccording to claim 1, wherein said individual filament yarns compriseextruded monofilament yarns and/or monotape yarns cut from an extrudedfilm.
 11. The synthetic turf according to claim 10 wherein the monotapeyarn of said composite yarn and the monofilament yarns of said compositeyarn are made of polyethylene.
 12. The synthetic turf according to claim1, wherein said tufts are arranged in rows which are situated on mutualdistances, measured from centre to centre, of between 8 and 24 mm. 13.The synthetic turf according to claim 1, wherein said tufts have anaverage height larger than 30 mm.
 14. The synthetic turf according toclaim 1, wherein it is top-dressed with a layer of at least oneparticulate material.
 15. The synthetic turf according to claim 14,wherein said particulate material comprises a polyolefin elastomer. 16.The synthetic turf according to claim 15, wherein the amount of fillermaterial in said particulate material is between 50 and 60% by weightand the amount of polyolefin elastomer in said particulate material isbetween 40 and 50% by weight.
 17. The synthetic turf according to claim14, wherein the particulate material is filled with filler materialselected from the group consisting of chalk and clay.
 18. The syntheticturf according to claim 14, wherein the particulate material comprises apolyolefin elastomer blend with EPM.
 19. The synthetic turf according toclaim 18, wherein the amount of EPM in said infill material is between0% and 20% by weight.
 20. The synthetic turf according to claim 14,wherein said particulate material is provided in the form of granules.21. The synthetic turf according to claim 20, wherein the granules havea diameter between 0.5 and 3.0 mm.
 22. The synthetic turf according toclaim 20, wherein the granules have a compound density of between 1.3and 1.5 kg/dm³ and a bulk density of between 0.6 and 1.0 kg/dm³.
 23. Acomposite yarn for use in a synthetic turf according to claim 1, whereinsaid composite yarn is formed by a fibrillated yarn twined together witha number of individual filament yarns, and wherein in said compositeyarn said fibrillated yarn is twined around the individual filamentyarns so that the composite yarn has an outer surface which is mainlyformed by the fibrillated yarn.
 24. The composite yarn according toclaim 23, wherein said composite yarn has a yarn number smaller than20000 dtex.
 25. The composite yarn according to claim 23, wherein saidcomposite yarn has a yarn number, at least 40% of which, is formed bysaid individual filament yarns, said fibrillated yarn forming at least30% of the yarn number of the composite yarn.
 26. The composite yarnaccording to claim 23, wherein said composite yarn comprises 4 to 10individual filament yarns.
 27. A synthetic turf comprising the compositeyarn according to claim
 23. 28. A natural grass system comprising thecomposite yarn according to claim 23 as tufts.
 29. The synthetic turfaccording to claim 1, wherein all of said individual filament yarns ofsaid composite yarn are made of polyethylene.